Windows down vs. AC

[Mach1E]

Do you have a source for those numbers? Or did you make them up?

I think it's highly likely that you're creating way more drag with the windows down than electricity consumption from running the AC. Air gets sucked in, swirls around, flaps the rear belts (seriously Ford, did no one test this?), and then is forced out as new air detaches into the interior. You want attachment, and for that air to hang on as long as possible, when the windows are open you're creating a swirling vacuumy mess around the car, this is the opposite of aerodynamic efficiency.

Given that the car was designed with CdA as a priority, it's really hard to see this any other way.

That said, if you want to open your windows, by all means open the windows. I do it too, some days it's nice to drive around with them down and the rear belt flapping .

Oh the 1/2 hp was completely made up. Was just using the same 1/2 hp drag example when someone talked about drag on a bicycle earlier.

Real hp losses from a modern A/C system are around 5-10 hp (proven by multiple dynos as well as drag races).

And windows down drag? Is in that same 5-10 hp (proven by multiple fuel efficiency real world tests).

Bottom line? This has been tested many times. Lower speeds? Windows more efficient.

Higher speeds? A/C more efficient.

But the difference isn’t that big. And who drives with the windows down at 80 mph anyways? If you were hypermilering, you’d probably just have them barely cracked at that speed! And probably only the front windows.

With the Mach E though, if the compressor is always running, may be a little different.

Sponsored

 

[ChasingCoral]

I suspect the buffering sound is a good indicator of the drag being produced. Of having the windows down makes too much noise, it’s probably producing more drag than the AC’s power use.

 

[babgvant]

Oh the 1/2 hp was completely made up. Was just using the same 1/2 hp drag example when someone talked about drag on a bicycle earlier.

Real hp losses from a modern A/C system are around 5-10 hp (proven by multiple dynos as well as drag races).

And windows down drag? Is in that same 5-10 hp (proven by multiple fuel efficiency real world tests).

Bottom line? This has been tested many times. Lower speeds? Windows more efficient.

In general, yeah violent agreement, slower speeds = windows, higher = AC. But where is the crossover? There is no way there is a one size fits all answer to this question. Every car has a different CdA, every car has a different window profile. It's simply not possible to say 40mph, done.

 

[SnBGC]

Oh the 1/2 hp was completely made up. Was just using the same 1/2 hp drag example when someone talked about drag on a bicycle earlier.

Real hp losses from a modern A/C system are around 5-10 hp (proven by multiple dynos as well as drag races).

And windows down drag? Is in that same 5-10 hp (proven by multiple fuel efficiency real world tests).

Bottom line? This has been tested many times. Lower speeds? Windows more efficient.

Higher speeds? A/C more efficient.

But the difference isn’t that big. And who drives with the windows down at 80 mph anyways? If you were hypermilering, you’d probably just have them barely cracked at that speed! And probably only the front windows.

With the Mach E though, if the compressor is always running, may be a little different.

The compressor isn't always running. Just when the HVB needs to be cooled. Depending on your location, it could be very frequent though...

 

[Mach1E]

In general, yeah violent agreement, slower speeds = windows, higher = AC. But where is the crossover? There is no way there is a one size fits all answer to this question. Every car has a different CdA, every car has a different window profile. It's simply not possible to say 40mph, done.

Someone could test it, but again, too many variables. A/C isn’t just “on or off.” Altitude and exterior temps matter and like you said, each car is different.

And are we talking front and rear windows?

If someone is hypermiling, it’s simple:

Shut off the A/C and barely crack the windows if you need to. Or even better, keep them closed and suffer……. But enjoy whatever bliss knowing that you’re the most efficient you can be!**

**This doesn’t work on me. Just like a “runners high,” I just ain’t wired that way.

 

[CarFanDan]

My annoyance with driving with windows down isn't the noise or loss of efficiency, it has to do with the privacy shade over the rear cargo area flops around, sometimes blocking my view out the rear. I like having the cover to keep people seeing what I have in the cargo area and I don't want to drive with it off.

 

[Mach1E]

My annoyance with driving with windows down isn't the noise or loss of efficiency, it has to do with the privacy shade over the rear cargo area flops around, sometimes blocking my view out the rear. I like having the cover to keep people seeing what I have in the cargo area and I don't want to drive with it off.

Sounds like you’re in a pickle…… gotta pick one or the other.

I took the shade off. The factory tint makes it hard to see what’s in the back anyways.

 

[GreaseMonkey]

 

[Mach1E]

Clearly better if he left his ac on

 

[Larry Paul]

Sounds like you’re in a pickle…… gotta pick one or the other.

I took the shade off. The factory tint makes it hard to see what’s in the back anyways.

I think that the cargo cover is the "canary in the coal mine". When it starts flopping around, the AC should be on and the windows should be closed.

FYI: I had put a hose and weight on the front edge of the cargo cover and I could drive at 65 and the cover just sat there...but my miles/kWh dropped... I now drive with AC on and the windows up nearly all the time now and my range increased dramatically and I removed the weight and hose.

This is the thread that inspired my design:

https://www.macheforum.com/site/thr...-better-cargo-cover-catches.5307/#post-436019

Sponsored